1. Field of the Invention
This invention relates to a medical leads having drawn-filled-tubing (DFT) conductors and more specifically to a medical lead having a low-profile DFT conductor to creating a medical lead with a reduced diameter and low resistance.
2. Discussion of the Related Art
A variety of medical electrode catheters are available today for the diagnosis and treatment of various disorders of the cardiovascular and neurological systems. These electrode catheters can be used to sense electrical activity within the body and to deliver different forms of energy to stimulate, ablate, cauterize or pace. Examples of medical catheters using electrodes include permanent and temporary cardiac pacing leads, electrophysiologic (EP) catheters, electrocautery probes and spinal stimulation catheters.
Conventional neural stimulation therapies rely on neurostimulation leads for stimulating various regions of the spinal cord that correspond to each physiologic region of the body. Placement of leads for both external and implantable RF stimulating devices is relatively simple for spinal cord stimulation. Here, a Tuohy needle is inserted into the spinal epidural space and the leads are placed adjacent to the targeted nerves addressing a specific painful region of the body. A relatively high power must be applied when directly stimulating the spinal nerves compared to the power required for peripheral nerve stimulation and deep brain stimulation. The high power consumption increases the frequency of the surgeries required for battery replacement. Thus, battery life is a major limitation for totally implantable systems. The relatively high resistance of conventional reduced diameter leads further increases the power necessary for spinal stimulation and further decreases the battery""s life. Therefore, a need exists for a lead body that more efficiently conducts electricity to reduce power consumption.
Further, spinal cord stimulation has limited effectiveness for certain pain conditions primarily due to limited accessibility to targeted nerves. In many cases where spinal cord stimulation is inadequate, spinal or peripheral nerves must be specifically stimulated to provide pain relief However, with existing technology, access to certain nerves can only be accomplished by a laminectomy, a surgery removing a portion of a vertibrae""s lamina, which results in significant scarring and patient discomfort. Therefore, a need exists for a lead that provides increased accessibility to perform a broader array of nerve stimulation.
Procedurally, spinal or peripheral nerve stimulation is more challenging than spinal chord stimulation. The spinal and peripheral nerves branch off of the spinal chord through the transverse foramen of the vertebrae. Spinal and peripheral nerve stimulation is necessary when a region of the body is affected that cannot be effectively stimulated via the spinal cord. To stimulate these nerves, a lead is inserted through the epidural space along the spinal chord and then turned laterally outward to track the branching nerves. To track these nerves requires a lead having a significantly smaller diameter than conventional stimulation leads. Therefore, a need exists for a reduced diameter lead to access the spinal and peripheral nerves.
The higher resistance of conventional reduced diameter leads also limits cardiac pacing, mapping and ablation catheters. Available reduced diameter leads may provide access to location within the heart and veins that would not otherwise accessible, but currently available leads do not provide the advantage of combining reduced diameter with reduced resistance. The advantages for cardiac pacing of reduced size include more efficient valve function when the lead passes through the valves in the heart and better access to smaller veins without compromising blood flow. Further, the reduced resistance provides the advantage of reducing the frequency of battery changes in the pacemaker. Thus, a need exists for a low resistance reduced diameter lead.
Sensing, in both cardiac and neurological applications, can be limited by the ability to effectively transmit signal from the patient to the medical device. Sensed events typically produce very week signals. Therefore, because of their higher resistance, conventional reduced diameter leads may limit the sensitivity of reduced diameter sensing leads. Thus, a need exists for a reduced diameter lead having lower resistance for application to neurological and cardiac sensing.
Conventional reduced diameter leads typically employ ribbon wire having a rectangular cross-section as conductors. These ribbon wire conductors provide adequate cross-sectional area for reduced resistance while maintaining a sufficiently low profile to reduce the overall diameter of the lead. These ribbon wires are typically solid stainless steel, MP35N, platinum/iridium, titanium and other biocompatible metals and alloys known to those skilled in the art. Although sufficient in most applications, these leads suffer from greater power consumption, as discussed above. Conventional leads have used DFT conductors at least in part for their reduced resistance relative to the above listed metals. The DFT previously used for leads has had a round cross-section, but the round cross-section limits the minimum size for a lead body""s construction. Thus, a need exists for a low-resistance lead body having a reduced profile.
The present invention meets the above needs and provides other improvements and advantages that will be recognized by those skilled in the art upon review of the following description and drawings.
A lead body in accordance with the present invention has a reduced diameter while retaining low resistance relative to a conventional reduced diameter lead. The low resistance of a lead in accordance with the present invention minimizes power consumption resulting in longer battery life and less frequent surgical interventions. The reduced diameter of a lead in accordance with the present invention allows access and reduces the steric hindrance created by having an implanted lead.
A lead body for a medical lead having an insulator and at least one low-profile drawn-filled-tubing conductor realizes the above improvements and advantages as well as other improvements and advantages. The lead body may include one or more lumen extending along its longitudinal axis. The low-profile drawn-filled-tube conductors are typically spirally wound within the insulator. Thus, the conductors are electrically insulated from one another within the lead body. The conductors typically extend from the distal end to the proximal end of the lead body. The conductors are typically electrically connected to one or more electrodes positioned toward the lead""s distal end. The conductors are typically electrically connected to one or more connector pins at the lead""s proximal end.
The low-profile drawn-filled-tubing conductors are composed of an outer casing and a core material. The low-profile drawn-filled-tube conductor typically has a cross-sectional shape that is crescent shaped, oval, trapezoidal, rectangular or similar low-profile cross-sectional shape. The outer casing is composed of stainless steel, MP35N, titanium, elgiloy or other suitable material. The core material is silver, gold, platinum. tungsten, tantalum copper or other suitable conductive material.
The method of the present invention provides an improved method for fabricating electrical stimulating leads. The lead body can, if desired, retain a central lumen through which a guidewire or stylet may pass. The present invention further provides a method for constructing a low resistance, leads of relatively small diameters. The method comprises heating an insulating material and embedding at least one low-profile drawn-filled-tubing conductor in the insulating material. By using the low-profile drawn-filled-tube conductor, the construction minimizes outside diameter and maximizes inner lumen space for over-the-wire delivery, stylet insertion, infusion of fluids, additional conductors and steering systems. The resulting leads provide enhanced sensitivity to low-level signals, providing improved output clarity and lower energy requirements when delivering stimulating currents to selected nerve tissue.